Families of firefighters who were killed in the World Trade Center collapse have asked government officials to investigate the main fire union's withholding of tens of millions of dollars in charity donations.

The union, the Uniformed Firefighters Association (UFA), says it welcomes the investigation by the New York state attorney-general and says it wants to distribute the money in the best way possible.

The dispute centres on the fire union's plan to hold onto most of the $60m it was given by the public in the wake of 11 September.

The search goes on for the remains of those who died

Each firefighter's widow would get a one-off payment of just $20,000 and then every year, they and each surviving child would get an additional $3,000 from the interest generated by the money being invested.

But the relatives of the 85 single firefighters who died in the World Trade Centre would get nothing at all.

The union's plan, say the firefighters families, is unfair and does not reflect the wishes of ordinary people who they believe donated the money to help them with their losses.

The row is the latest in a series of fights between charities and relatives over who should get financial help and when.

The families say the fire unions should keep only about $3m and distribute the rest, and that the union is humiliating them by implying that they could not manage a large amount of money.

The attorney-general's office says it will look into the dispute and the union's plans for the money it was given.